Olefins, also commonly known as alkenes, are important items of commerce. Their many applications include employment as intermediates in the manufacture of detergents, as precursors to more environmentally friendly refined oils, as monomers, and as precursors for many other types of products. An important subset of olefins is alpha olefins. One method of making alpha olefins is via oligomerization of ethylene, which is a catalytic reaction involving various types of catalysts and/or catalyst systems. Examples of catalysts and catalyst systems used commercially in the oligomerization of ethylene include alkylaluminum compounds, certain nickel-phosphine complexes, a titanium halide with a Lewis acid (e.g., diethyl aluminum chloride), a selective 1-hexene catalyst system containing a chromium containing compound (e.g., a chromium carboxylate), a nitrogen containing ligand (e.g., a pyrrole), a metal alkyl (e.g., alkyl aluminum compounds), and selective trimerization and/or tetramerization catalyst systems using a metal complex of a compound having a diphosphinylaminyl group.
Several non-commercial ethylene oligomerization catalyst systems are based upon metal complexes of pyridine bis-imines, and metal complexes of α-diimine compounds having a metal complexing group. These catalyst systems typically use an alkyl aluminum compound (e.g., aluminoxane) to activate the metal complexes for olefin oligomerization.
Applications and demand for olefins (e.g., alpha olefins) continue to multiply, and competition to supply them correspondingly intensifies. Thus, additional novel and improved catalyst systems and methods for ethylene oligomerization are desirable.